Strings in Java

Strings in Java

In the Java programming language, a string is nothing more than a sequence of characters. It is the most used object. The Java String class has many methods that are used for various manipulations. It is immutable, that is, its value cannot be changed. A string is equivalent to an array of characters.

Create a string in Java

We can create a string using 2 different methods:

  • Using a literal string
  • Use a new keyword

Create a string using a string literal

This is the most direct way to create a beautiful one in Java. We can create a string by enscasing the value in quotation marks. Here, the string “value” variable contains the string named “Java language”String value = “Java language”;

When we create a string literal, JVM first checks the “string constant pool” to see if the string exists. If it does not exist, the JVM creates a new string instance, otherwise only a reference to the pooled instance will be returned. For example, in the case below, both string objects have the same value. Therefore, only one object is created (that is, s1) and s1 will have the reference to s2. This means that no matter how many string variables we create with the same value, only one instance will be created in the string constant pool.

“String constant pool” is nothing but the special memory to hold string objects.https://57362150bd7f309b09b86e21f96387a8.safeframe.googlesyndication.com/safeframe/1-0-38/html/container.htmlString s1 = “Java language”; String s2 = “Java language”;

Chaîne en java

Create a string using the new keyword

When we want to have 2 different objects containing the same string value, we create a string using the Nine (ve) keyword as described below. In this case, JVM creates 2 different string objects in heap memoryString s1 = new String(“Java”);String s2 = new String(“Java”);

Chaîne en java

Java String Methods

The java.lang.String class supports various methods that are used for different string manipulations as described below:

deliverydescriptionparameters
char charAt (int index)Returns the character at the specified index of the input stringindex – the index value of the string
int codePointAt (int index)Returns the unicode value of the character at the specified indexindex – the index value of the string
int codePointBefore (int index)Returns the unicode value of the character present before the specified indexindex – the index value of the string
int compareTo (string anothertring)Compares 2 strings based on the unicode value of the characters and returns a negative value if it precedes the argument string, otherwise returns positive. The return value is 0 if the two strings are equalanotherstring – string to compare with string object
int compareToIgnoreCase (string anothertring)Similar to the compareTo method except that it ignores case.anotherstring – string to compare with string object
Concat String (String String)Concatenates two string valuesstr – The string to concatenate with the value of the string object
boolean contains (CharSequence c)Checks whether the string contains the specified character sequence and returns true if presentc – Sequence of characters to search for in the string
boolean contentEquals (CharSequence c)Checks whether the string contains the exact character sequence and returns true if presentc – Sequence of characters to search for in the string
boolean contentEquals (StringBuffer sb)Checks whether the string contains the specified string buffer and returns true if presentsb – String buffer contents
boolean endsWith (string suffix)Checks whether the string ends with the specified suffix and returns true if presentsuffix – the suffix to save in the string
Boolean is equal to (Object obj)Checks the similarity of the string object with the object passed in and returns true if equalobj – The object to compare
boolean equalsIgnoreCase (string)Compares two strings independently ignoring case and returns true if the two strings are equalstr – The string to compare
int indexOf (int ch)Returns the index of the first occurrence of the specified Unicode character in the stringch – unicode value of the character
int indexOf (str string)Returns the index of the first occurrence of the specified substring in the stringstr – the substring value present in the string
Boolean isBlank ()Returns true if the string is empty or contains only blank spaces
Boolean isEmpty ()Returns true if the string is empty (that is, the length is 0)
int lastindexOf (int ch)Returns the index of the last occurrence of the specified Unicode character in the stringch – unicode value of the character
int lastindexOf (str string)Returns the index of the last occurrence of the specified substring in the stringstr – the substring value present in the string
length int ()Returns the length of the string
Boolean matches (String regex)Returns true if the string matches the specified regular expressionregex – The regular expression to check
String repetition (integer)Concatenates the string based on the numbercount – number of times to concatenate the input string
Replace string (char oldchar, char newchar)Returns the new string by replacing all occurrences of the character with the new characteroldchar – character
to replace newchar – character to replace
String [] split (string regular expression)Divides the string based on the regular expression. It returns an arrayregexp – delimiter to divide the string
String [] split (string regular expression, int limit)Divides the string based on the regular expression and the number of times it should be appliedregexp – delimiter
to divide the limit string – number of times the pattern should be applied
boolean startsWith (string prefix)Checks whether the given string begins with the specified prefix. Returns true if presentprefix – the prefix to register in the string
boolean startsWith (String prefix, int tooffset)Checks whether the given string begins with the prefix specified based on the tooffset parameter.prefix – the prefix to
be saved in the tooffset string – the index from which to start the search
Twine strip ()Returns a string with all spaces removed, both start and end
ChainLeading Band ()Returns a substring of the string with all leading spaces removed
Chain bandReturns a substring of the string with all trailing spaces removed
CharSequence subSequence (int startIndex, int endIndex)Returns a sequence of characters in the string based on the start and end indexstartIndex – the index from which the substring is to be retrieved
endIndex – the index up to which the substring is to be retrieved
String subString (int startIndex)Returns a substring of the string based on the starting indexstartIndex – the index from which the substring is to be retrieved
String subString(int startIndex, int endIndex)Returns a substring of the string based on the start and end indexstartIndex – the index from which the substring is to be retrieved
endIndex – the index up to which the substring is to be retrieved
char [] to CharArray()Converts the string to a character array
String toLowerCase()Converts all characters in the string to lowercase
String toLowerCase (locale)Converts all characters in the string to lowercase based on local ruleslocale – the local rules to apply
String toString ()Returns the string itself
ToUpperCase string ()Converts all characters in the string to uppercase
String toUpperCase (locale)Converts all characters in the string to uppercase based on local ruleslocale – the local rules to apply
Chain cut ()Returns a string with all leading and trailing spaces removed
String formatString (string format, object … args)Returns a formatted string based on format and argumentsformat –
format specifier args – arguments referenced by the format specifier
Jointure de chaîne (délimiteur CharSequence, éléments CharSequence …)Joint les éléments de la séquence de caractères à l’aide du délimiteurdelimiter – le délimiteur à joindre
elements – les éléments de chaîne à joindre
Chaîne valueOf (booléen b)Renvoie la représentation sous forme de chaîne de l’argument booléen. Si true est passé, renvoie trueb – valeur booléenne vraie ou fausse
Chaîne valueOf (char c)Renvoie une représentation sous forme de chaîne de l’argument de caractèrec – caractère
Chaîne valueOf (char [] data)Renvoie une représentation sous forme de chaîne de l’argument du tableau de caractèresdata – tableau de caractères
Chaîne valueOf (double d)Renvoie une représentation sous forme de chaîne de l’argument doubled – valeur double
Chaîne valueOf (float f)Renvoie une représentation sous forme de chaîne de l’argument floatf – valeur flottante
Chaîne valueOf (int i)Renvoie une représentation sous forme de chaîne de l’argument entieri – valeur entière
Valeur de chaîne IOf (long l)Renvoie une représentation sous forme de chaîne de l’argument longl – valeur longue
Chaîne valueOf (Object obj)Renvoie la représentation sous forme de chaîne de l’argument objetobj – objet
Chaîne valueOf (char [] data, int offset, int count)Renvoie une représentation sous forme de chaîne de l’argument de tableau de caractères de sous-chaîne spécifique en fonction du décalage et du nombredata – tableau de caractères
offset – index de début
count – longueur de la sous-chaîne

Example: Using the length(), charAt(), and indexOf() methods

The following example shows you how to retrieve a character at a particular index, get the length of a string, and retrieve the index of a particular character.public class StringDemo2{ public static void main(String[] args){ String s1 = new String(“Java tutorial”);System. out. println(“The character at index 6 is : ” + s1. charAt(6));System. out. println(“The length of the input string is : ” + s1. length());System. out. println(“The index of letter ‘v’ is : ” + s1. indexOf(‘v’)); }}Output:The character at index 6 is : uThe length of the input string is : 13The index of letter ‘v’ is : 2

Example: Using compareTo(), contentEquals(), and contains()

This example shows a comparison of 2 strings in Java

  1. compareTo() here returns a positive integer since the input string succeeds the argument string.
  2. compareToIgnoreCase() returns 0 because the two strings are equal regardless of case.
  3. contains() returns true because the input string contains the argument string
  4. contentEquals() returns false because the input string does not contain the exact argument string.

public class StringDemo2{ public static void main(String[] args){ String s1 = new String(“Java tutorial”);System. out. println(“Comparison of input string with argument is : ” + s1. compareTo(“C++”));System. out. println(“Comparison of input string with argument ignoring case is : ” + s1. compareToIgnoreCase(“JAVA TUTORIAL”));System. out. println(“Output of contains method: ” + s1. contains(“tutorial”));System. out. println(“Output of contentEquals method: ” + s1. contentEquals(“Java”)); }}Output:Comparison of input string with argument is : 7Comparison of input string with argument ignoring case is : 0Output of contains method: trueOutput of contentEquals method: false

Example: Using equals ()

The first output is false because the case does not match even if the content is the same. The second output is true since the content and case match.

The third output is false because the two contents are different.public class StringDemo3{ public static void main(String[] args){ String s1 = “java tutorial”; String s2 = “Java Tutorial”; String s3 = “java tutorial”; String s4 = “Tutorial cup”;System. out. println(s1. equals(s2));System. out. println(s1. equals(s3));System. out. println(s1. equals(s4)); }}Output:falsetruefalse

Example: String Concatenation

One can concatenate 2 strings in Java using concat() method of the Java String Class. “+” Is also used to concatenate 2 or more strings that are normally used in print instructions. When concatenating 2 strings, space is not included between the strings. In the example below, the string s3 contains the concatenated value of s1 and s2 that is used with a new string in the print statement.

We can also concatenate 2 strings in Java using the join() method. This will join the passed words in the argument with a specified delimiter.public class StringConcat{ public static void main(String[] args){ String s1 = “Hello,”; String s2 = “how are you”; String s3 = s1. concat(s2);System. out. println(s3 + ” today”);System. out. println(s1. join(“,”, “welcome”,”to”,”tutorialcup”)); }}Output:Hello,how are you todaywelcome,to,tutorialcup

Example: Java program to convert a string between uppercase and lowercase

public class StringCase{ public static void main(String[] args){ String s1 = “Welcome to tutorialcup”;System. out. println(“Convert to lower case: ” + s1. toLowerCase());System. out. println(“Convert to upper case: ” + s1. toUpperCase()); }}Output:Convert to lower case: welcome to tutorialcupConvert to upper case: WELCOME TO TUTORIALCUP

Example: Using a Substring in Java

We can retrieve part of the string in Java using the substring method. The index value starts at 0.public class StringDemo3{ public static void main(String[] args){ String s1 = “java tutorial”;System. out. println(s1. substring(3));System. out. println(s1. substring(1, 10)); }}Output:a tutorialava tutor

Example: Using Division and Replacement

Split is another method of String most commonly used in Java. In this example, we first split the input string using the “” delimiter. Therefore, this prints each word separately. Next, we divide according to the delimiter but specify the limit to 2, which means that it only divides into two string array values.

In the first replacement example, we replace the individual character. In the next one, we replace the sequence of characters.public class StringDemo4{ public static void main(String[] args){ String str1 = “Welcome to java programming”;System. out. println(“Split output using delimiter:”); Split using only delimiter String[] arrval = str1. split(” “); for(int i=0;i<arrval. length;i++){System. out. println(arrval[i]); }System. out. println(“\nSplit output using delimiter and limit:”); Split using delimiter and limit String[] arrval2 = str1. split(” “, 2); for(int i=0;i<arrval2. length;i++){System. out. println(arrval2[i]); } System. out. println(“\nReplace output with character:”); Replace character String str2 = str1. replace(‘j’, ‘J’);System. out. println(str2);System. out. println(“\nReplace output with character sequence:”); String str3 = str1. replace(“java”, “javascript”);System. out. println(str3); }}Output:Split output using delimiter:WelcometoJavaprogrammingSplit output using delimiter and limit:Welcometo java programmingReplace output with character:Welcome to Java programmingReplace output with character sequence:Welcome to javascript programming

Example: Java format string

We can format any data type to a string using the format method. Here we use string (“%s”), float (%f”), and boolean (“%b”) as examples.public class StringFormat{ public static void main(String[] args){ String str = “Java”; String formatstring1 = String. format(“Programming language is %s”,str); String formatstring2 = String. format(“Float value is %f”, 55.6789); String formatstring3 = String. format(“Boolean value is %b”, true);System. out. println(formatstring1);System. out. println(formatstring2);System. out. println(formatstring3); }}Output:Programming language is JavaFloat value is 55.678900Boolean value is true

conclusion

In this tutorial, you learned about String in Java, different ways to create it, and different string methods as well as example

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